After some time measuring and staring at graphs, I'm finally ready to post an update (yeah!)
First, I must confess that it's been difficult to stay focused on this project, with the room being fully functional and what not. I've watched and number of great movies with family and friends already, everyone seems to love the space as it is, but I push on.
Cool, so below are my results for the Nyal Mellor criteria Helpful Fred posted:
Here's the SPL of my room with nothing playing (I disconnected the output cable). From looking around online, it seems that this might be RC35. To be honest, I'm a bit surprised that it's not lower, with the decoupled walls and ceiling. What are other people getting? As for the spike around 60Hz, I think that the the heat pump running - the unit is right outside this room in the basement...
B: Reflected Sound Energy Time Curve, 0‐40ms
- L & R speakers visually identical
- ~10dB reduction in energy level by 40ms
- Clear decrease in energy over the 40ms
- Peaks smooth in pattern and density
The two pictures below are for all three front speakers - first with no smoothing and then with 1ms smoothing. I can't say for sure, but it seems OK to me...???
C: Low Frequency Decay Times
- Resonances from 35Hz 300Hz should not extend beyond 350ms before decaying into the noise floor or reaching a level of 40dB.
- Below 35Hz this standard is relaxed to 450ms.
I usually look at the waterfall graphs, but since Nyal's article uses spectrograms, I'll show them too. Note, for each speaker, both the sub and the speaker are playing.
First the waterfalls (spectrograms next):
And now the spectrograms (waterfalls before):
This Bass Integration Guide
by Paul Spencer suggests that there should be a 20dB decay after 150ms. I couldn't figure out how to get GIMP to plot the -20dB line, but I think that it's not too hard to eyeball...
D: Midrange Decay Times T20, T30, T60
- T60 between 0.2 and 0.5s
- T20, T30 deviation
I'm not sure if I generated these graphs correctly, but I think they might indicate an overly short decay for the midrange (250Hz - 4000Hz) - right?
E: Midrange Frequency Response
- L speaker within +/‐3dB at 1/3rd octave
- R speaker within +/‐3dB at 1/3rd octave
- No deviation greater than 3dB between L/R speakers
OK, so my speakers seem to be more than +-3dB, it's more like +-5db
F: Low Frequency Response
- Within +/‐10dB at 1/24th octave
- Within +/‐5dB at 1/3rd octave
For the 1/24th octave, 108Hz goes from 80-105dB, 169hz goes 84-112dB, and 183Hz goes 78-107dB
For the 1/3rd octave, 173Hz goes 90-104dB and 194Hz goes 87-103dB
G. Room Size and Construction
- Physical dimensions: Size of room 224sq ft to 475 sq ft, Volume of room 1,750 cu ft to 4,750 cu ft
- Dimensions lack common divisors
- (2x) layers of 5/8 gypsum board
- Surfaces are constructed using similar methods
My room is roughly 315 sq ft and 2700 cu ft
Calculating if the room has common divisors is difficult to do since the walls/ceiling aren't perfectly straight/level - no single measurement can be used. Also, my room has a bump-out behind the screen, where it's under a a bay window, so the length of the room is an extra 2.5 feet in the area.
Yes, the room is DD+GG on top of decoupled walls and ceiling.
OK, so this was a much longer post than I expected. I actually kind of knew it would be, as I spent some time yesterday thinking about all the pics that would have to be posted
BTW, I tried to test the tweeter drop-off issue/concern from before. To be honest, I'm not sure what the concern is, other than it looks like tweeter has little output from beyond 10kHz. I'm not sure if the below graph helps, but it seems that *all* the speakers are dropping off in that range. Now, admittedly, this is a farfield measurement (as are all the others), so maybe this indicates too much high-freq absorption - would putting scrim/plastic/paper over the linacoustic help?
Anybody have any advice for how to make this room sound better?